The present invention relates generally to the production of carbon black through pyrolytic distillation of scrap tires. More specifically, the present invention relates to a used tire pyrolysis system and method that incorporates a novel feed tube and zoned heating of tire scrap material to extract carbon black, scrap steel, heating oil and gas.
As the supply of available landfill space decreases, environmentally sensitive disposal of consumed vehicle tires is become an ever-increasing problem. In the U.S. alone, over 280 million vehicle tires are scrapped and shipped to landfills each year. Although some of the used vehicle tires are recycled to be used in pavement and others are burned as boiler fuel, more than 80% of used vehicle tires end up being deposited in landfills. Discarding spent vehicle tires in landfills has been recognized as a significant waste of recyclable resources. For many years it has been known that used vehicle tires can be recycled by pyrolysis to obtain valuable by-products that can be sold and reused. Pyrolysis, generally speaking, is a thermal distillation or decomposition of a substance. In the case of used vehicle tires, this process is carried out in the absence of oxygen and at temperatures generally between 500.degree. C. and 800.degree. C.
The process of recycling used tires by pyrolysis allows the recovery of substantial amounts of oil, gas, carbon black and scrap steel. In particular, it is expected that using the apparatus described herein, it will be possible to recover approximately 35 tons of carbon black and 10 tons of scrap steel from 100 tons of shredded vehicle tires.
Although many machines have been designed to recycle used tires through pyrolysis, none have been entirely successful. One problem with many previous machines involves the presence of particulate matter in the gas that is evolved from the tires. Particulate matter--primary carbon dust and glass fiber, accumulates in fittings, vents and flame arrestors, which can obstruct passages and create substantial danger of explosion.
Another of the difficulties of the present methods to recycle used tires through pyrolysis is that the solid carbon product, carbon black, obtained is outside of the specification for most commercial grade carbon black and is therefore not commercially usable. Thus, in order to produce commercial grade carbon black it is necessary to invest thermal energy to the recovered oil obtained through pyrolysis. As can be understood, it would be much more energy efficient to directly recover a commercial grade carbon black through the pyrolysis of used vehicle tires.
Another drawback to known pyrolysis machines involves oil contamination in the carbon black which destroys the commercial value thereof. In order to produce high quality carbon black, virtually all oil must be removed. In known pyrolysis machines, the oil vapor released from the pyrolyzed material is drawn, at least partially, through or past the carbon black product, thus contaminating it with oil residue.
Handling the shredded tire pieces has also presented substantial challenges in known pyrolysis systems. The residual steel strands and natural stickiness of the heated rubber combine to make transporting the shredded tires to be pyrolyzed a significant challenge. For example, many known methods utilize a rotating screw to feed the shredded tires into a kiln in which the pyrolysis process occurs. Due to the inherent properties of the shredded tires, the persistent problem with known machines is "baling-up" of the shredded tires within the screw conveyor leading to jamming of the screw auger used to convey them
Therefore, it is an object of the present invention to provide a pyrolysis system that efficiently and effectively feeds shredded vehicle tires into a rotary kiln in which the pyrolysis process occurs. It is an additional object of the present invention to operate the process of the pyrolysis system in a separate zoned manner to most efficiently process the vehicle tires. It is another object of the invention to operate the process in separate zoned areas, each of which operates at a distinct temperature to maximize the efficiency of the pyrolysis process. It is a further object of the invention to efficiently separate the recovered carbon black from the scrap steel at the end of the rotary kiln. Further, it is an object of the present invention to evacuate the oil-containing producer gas from within the rotary kiln at a position spaced from the discharge end of the rotary kiln to prevent contamination of the carbon black.